1. Field of the Invention
The present invention relates to an improvement of an oxygen sensor, comprising electrodes, a sensor element which generates an electromotive force or which changes its electric resistance value between the electrodes depending on oxygen concentration of a gas to be measured, electrode terminals arranged on the sensor element and connected to the electrodes, and a metallic accommodating member accommodating the sensor element.
2. Related Art Statement
Heretofore, the above type of oxygen sensor 20 has ceramic powder 30 filled and compressed between a metallic cap 10 and a sensor element 12, and the compressed ceramic powder 30 fixes the sensor element 12 and separates air from the gas to be measured, if air is used as a standard oxygen atmosphere for the sensor element 12, as shown in partial crosssection in attached FIG. 2a.
The cap 10 has a rubber plug 14 at its upper open end portion opposite to a housing 4 for receiving lead wires 13 therethrough. The plug 14 is fixed at the position by caulking the cap 10 to seal the cap 10. Female contacts 15 are arranged at the end of the lead wires 13 for electrically connecting an electrode terminal 17 of the sensor element 12 and the female contacts 15 in a ceramic housing 16.
Namely, as shown as exploded perspective view in FIG. 2b, the female contact 15 per se has a resilient function and is accommodated in the ceramic housing 16, so that the female contact 15 and the ceramic housing 16 are made integral with each other to form an integral body, and the sensor element 12 is inserted in the integral body to attain electrical connection of the female contact 15 and the electrode terminal 17 of the sensor element 12 by means of the resilient function of the female contact 15 per se.
However, this type of oxygen sensor 20 has a drawback in that a high compressing pressure cannot be obtained, so that electrical connection between the electrode terminal 17 and the female contact 15 becomes unstable, because the electrode terminal 17 and the female contact 15 are contacted by means of the resilient function of the female contact 15 per se.
The oxygen sensor 20 has also a drawback in that, when inserting the sensor element 12 in the integral body, the plating layer provided on the female contact 15 at which the electrode terminal 17 of the sensor element 12 contacts, is rubbed against the end portion and the electrode terminal 17 of the sensor element 12 and peeled off therefrom at the portion A shown in FIG. 2. As a result, a drawback arises also in that the electrical connection between the female contact 15 and the electrode terminal 17 becomes bad by fretting corrosion etc., due to vibration and/or humid atmosphere during a long period of use of the oxygen sensor.